1. Field of the Invention
The present invention relates to a lens barrel for a zoom lens and other lenses, and an imaging apparatus, such as a digital single lens reflex camera, including the lens barrel.
2. Description of the Related Art
An example of the lens barrel of this type of related art is described, for example, in JP-A-11-311733. JP-A-11-311733 describes a zoom lens in which the amount of travel in a focusing operation on the telescopic side differs from that on the wide-angle side. The zoom lens described in JP-A-11-311733 is “an inner-focus and rear-focus zoom lens including a zooming operation ring that is rotated for a zooming operation, a focus operation ring that is rotated for a focusing operation, a rotatable and translatable tube that rotates and translates back and forth when the zooming operation ring is rotated, the rotation and translation caused by a first cam mechanism that cooperates with a fixed member and to which the rotation of the zooming operation ring is transmitted, a rotatable tube that engages projections provided on the outer circumferential surface of the rotatable and translatable tube so that the rotation of the rotatable and translatable tube is transmitted to the rotatable tube, a first lens group that is translated back and forth while being linearly guided along a first guide member when the rotatable tube rotates, the translation caused by a second cam mechanism that cooperates with the rotatable tube, a second lens group that is translated back and forth when the rotatable and translatable tube rotates, the translation caused by a third cam mechanism that cooperates with the rotatable and translatable tube, and a second guide member that is integrated with the focus operation ring, the second guide member linearly guiding the second lens group when the rotatable and translatable tube rotates and rotating the second lens group when the focus operation ring rotates so as to translate the second lens group back and forth under the guidance of the third cam mechanism.”
According to the thus configured zoom lens described in JP-A-11-311733, when the zooming operation ring is rotated in the zooming operation, the first cam mechanism rotates and translates the rotatable and translatable tube back and forth. Further, when the rotatable and translatable tube rotates, the third cam mechanism linearly translates the second lens group to a predetermined position under the guidance of the second guide member. The rotation of the rotatable and translatable tube is transmitted through the projections to the rotatable tube outside the rotatable and translatable tube. When the rotatable tube rotates, the second cam mechanism translates the first lens group to a predetermined position under the guidance of the first guide member. On the other hand, when the focus operation ring is rotated in the focusing operation, the second guide member rotates the second lens group, and the third cam mechanism translates the second lens group back and forth by an amount of travel according to the zooming position. The focusing operation is thus completed.
The zoom lens described in JP-A-11-311733, however, has the following problem. That is, since a second zoom synchronized lever connects a cam ring to a cam ring for a fourth lens group, the space is used in a manner with significantly poor efficiency. One reason for such a problem is that since the rotation angle of the zooming operation ring typically ranges from approximately 70 to 120 degrees, a significantly large space is necessary to rotate the sturdy second synchronized lever within the angular range. A second reason for the above problem is that although a larger amount of travel of the first lens group may require a larger amount of travel of the cam ring, the fact that the second zoom synchronized lever is supported by the cam ring limits the amount of travel of the first lens group to a value determined by the amount of travel of the cam ring for the fourth lens group (the amount of travel of the third lens group) and the length (total length) thereof. Such limitation prevents reduction in size of the entire zoom lens, and also prevents improvement in optical performance.
Recent digital single lens reflex cameras have significantly advanced in terms of their compactness, resolution, and performance. A typical structure for achieving compactness is often configured in such a way that at least two cam rings are rotated and one of the cam rings is translated in the optical axis direction. Such a structure may be essential to reduce the size of the barrel while maximizing the amount of lens travel and reduce the zooming torque. A challenge in the design phase is a connection mechanism for rotating the cam rings when the zooming operation ring is rotated, because the connection mechanism typically takes up a large space and it is therefore necessary to provide a space for such a large connection mechanism.
It has been significantly important to solve the above problems and design and manufacture a compact lens barrel with high performance at a low cost.